Monday, March 19, 2007

Spindle Neurons and Science Writing

In the wake of a hyperbolic new article (Freedberg & Gallese, 2007) on trendoid mirror neurons, Neurobloggy Land has noted that spindle neurons (aka von Economo neurons) are competing for attention.

In Neuroscience and Science Writing, Jonah at The Frontal Cortex argues that colorful, metaphoric language is suitable for popular science writing, even though it may lack precision (and may even be scientifically inaccurate, as I shall argue below). The case in point here is a post claiming that spindle neurons "convey our social emotions across the entire brain." Natasha commented on the use of language, saying:
But this doesn't as a statement make any sense "their antenna-like cell body is able to convey our social emotions across the entire brain". Neurons fire action potentials and the best they can conduct is patterns of firing or epsps/ipsps. They can't convey something as complex as 'social emotions'! That sounds like very sloppy thinking, even if they conduct something, some pattern, some information, to other brain regions its not 'saturating other brain regions with the same feeling'.
Jonah responded to this criticism:
The comment, of course, is true. Neurons traffic in electricity and neurotransmitter. A squirt of dopamine isn't a feeling; it's just a squirt of dopamine.

. . .

And yet, I'm also not planning on abandoning my "reification" of brain cells anytime soon. I still think it's acceptable to refer to spindle cells as conveyors of social emotion, or to allude to dopamine neurons as representing feelings of pleasure. Although no subjective experience - like a feeling - can be literally reduced into a discrete neural circuit, I think such writerly approximations are acceptable. ... It's a necessary inaccuracy, a way of collapsing different levels of scientific description.
He went on to suggest that
a significant and growing body of evidence suggesting that our spindle neurons are involved in the transmission of social emotion and social intuition.
Not to be a snarky cranky critic or anything, but I disagree about the strength of that evidence (and responded thusly)...
Based on the cited comments from Allman et al. (2005), I can see why you might think that spindle neurons transmit social emotions. However, their Trends in Cognitive Sciences article was categorized under the Opinion section with the title, "Intuition and autism: a possible role for Von Economo neurons" [my emphasis]. The article is highly speculative. No neurophysiological studies of spindle cells have ever been conducted, for obvious reasons (no single-unit recording in chimps or humans or humpback whales). So nothing is known about their physiological properties. Nothing is even known about their target projection sites (Allman et al., 2005): "However, it is not known where the VENs ultimately project."

Neuroanatomical data suggest that the dendritic structure of VENs (von Economo neurons) makes them "computationally simple compared with pyramidal neurons" (Watson et al., 2006), at least for their inputs.

Finally, humpback whales have many spindle cells (Hof et al., 2006), but they're largely solitary creatures (Valsecchi et al., 2002):

"These findings suggest that, if any social organization does exist, it is formed transiently when needed rather than being a constant feature of the population, and hence is more likely based on reciprocal altruism than kin selection."

...with all due respect to science writers (outside the blog format) who are faced with inadequate space, editors who push to simplify, and deadlines.

Oh, and Patrick Hof, another expert spindle cell neuroanatomist who is not John Allman, is more circumspect about their functional significance.

And while we're at it, check out the neurocritical comment by tfman on the study that sparked the debate, a recent article about spindle cells and humor (Watson et al., 2007):

Hey.. I read this paper, and for what its worth, seems to me the entire bloody brain is sensitive to humor (green in Figure 4), including the (unsexy) temporal cortex. bilateral inferior frontal gyri and more.

But wait, activity that correlates with subjective feeling of funniness (fig 2,3) is also found in white matter (!!) and the ventricles (!) so how much can we trust the rest of the data? (and SPM has the unsettling tendency to project both sulcal and gyral activity to the surface of the cortex in their graphical displays, which is misleading)

So lets put some of this in context: Von Economo cells are part of a larger system (just like mirror neurons are part of larger systems), and possible involved in the integration of information that is needed to 'get' jokes (especially verbal ones). Focusing on them, for whatever reason, in this article is likely to be as an arbitrary political decision akin to those papers that focus on "mirror neuron areas" when its clear the entire brain is involved in imitation.

. . .


References

Allman JM, Watson KK, Tetreault NA, Hakeem AY. (2005). Intuition and autism: a possible role for Von Economo neurons. Trends Cog Sci. 9:367-73.

Freedberg D, Gallese V. (2007). Motion, emotion and empathy in esthetic experience. Trends Cog Sci. Mar 6; [Epub ahead of print]

Hof PR, Chanis R, Marino L. (2005).Cortical complexity in cetacean brains. Anat Rec A Discov Mol Cell Evol Biol. 287:1142-52.

Valsecchi E, Hale P, Corkeron P, Amos W. (2002). Social structure in migrating humpback whales (Megaptera novaeangliae). Mol Ecol. 11:507-18.

Watson KK, Jones TK, Allman JM. (2006). Dendritic architecture of the von Economo neurons. Neuroscience 141: 1107-12.

Watson KK, Matthews BJ, Allman JM. (2007). Brain activation during sight gags and language-dependent humor. Cereb Cortex 17:314-24.

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